Atherosclerotic calcification has profound effects on arterial wall rigidity and is closely associated with morbidity and mortality. However, the mechanisms of dystrophic calcification remain poorly understood. A recent in vitro study demonstrated that vesicles isolated from atherosclerotic human and rabbit aortas can initiate calcification. It remains to be established: 1) whether hyperlipidemia, which causes atherosclerotis, can promote calcification through the production or activation of calcifiable vesicles and 2) how vesicle-mediated calcification is regulated through an active process. To address these issues, the present proposal will focus on the following Specific Aims: 1) To support the role of vesicles in calcification by evaluating the hypothesis that calcifiability of vesicles precedes and progressively increases with aortic calcification during atherogenesis. At different periods of time, aortic vesicles will be isolated from the control and experimental animals and compared for their calcifiability. Fourier transform spectroscopy will be used to characterize the types and to measure the amount of mineral deposited in aorta and by isolated vesicles. A similarity in the amounts and types of mineral deposited by vesicles and in aortas would strongly implicate vesicles in atherosclerotic calcification. 2) To test the hypothesis that vesicle-mediated calcification is closely regulated by cellular, matrix, and vesicle constituents. Cholesterol and its derivatives hydroxycholesterol and deoxycholate detergent known to stimulate cell- and vesicle- mediated calcification will be used to study the mechanisms whereby hyperlipidemia can lead to calcification. The effects of macrophage products such as osteopontin on vesicle calcification and tumor necrosis factor (TNF-alpha) on pathogenesis of calcifying vesicles will be investigated for a better understanding of the active process involved in vesicle-mediated calcification. A long-term goal of the project is to identify factors that initiate and control dystrophic calcification, thereby contributing to the knowledge that may lead to the prevention and treatment of atherosclerotic calcification.